The satellite television reception only (TVRO) industry is presently experiencing an ever-increasing growth in demand for systems to provide the tremendous array of programming available to the consumer. As is well known in the art, there is a band of satellites in geo-synchronous orbit over the equator, and each of these satellites has a number of transponders which transmit an RF signal containing video and audio information for a television program. This information can be received by an antenna comprised of a dish mounted to a support (generally a pole) with the dish being canted with respect to the pole and aligned such that as it is driven from side-to-side it moves its focal axis through the "arc" of satellites. As can be appreciated by those of ordinary skill in the art, the geometry involved can be quite complicated in that the canting of the dish with respect to the pole varies with respect to the geographic location of the dish (commonly referred to as the declination angle) and the alignment of the pole and dish is critical to ensure that movement of the dish in the azimuth direction moves the dish along the arc.
Because of the rapid growth in this market, there are not nearly enough skilled people to attend to the installation of antennas in a proper manner to ensure optimum performance. Furthermore, to the extent that these installers are available, they are in high demand and their time can be quite expensive, thus adding significantly to the cost of an installed TVRO system. Still another problem is that typically a linear actuator, or linear jack, is mounted between the support pole and the dish and is used as the drive mechanism to drive the dish. These linear actuators are no more than jacks which extend and retract in piston-like fashion. As a result of this translation of linear to rotational movement, there is no direct relationship between jack travel and arc degrees through which the dish moves. In other words, one inch of jack travel does not correspond to a given number of degrees of arc movement for the antenna as it depends upon the jack mounting, and the location of its travel at which the measurement is taken. This non-linear relationship makes it somewhat difficult to repeatedly, automatically move between satellites without individually programming in each satellite after the antenna and receiver are installed.
Still another problem experienced in TVRO system installations is that the antenna, being a mechanical structure, has a tendency to shift its adjustment over time due to weathering, and other factors. Therefore, to maintain optimal reception, most antennas should be readjusted periodically to ensure that they remain "on the arc" and that the best available signal is received from each of the satellites. Of course, this readjustment can be expensive but with antennas of the prior art, there is not much choice.
To solve these and other problems with prior art antennas and receivers, the inventors herein have succeeded in developing a receiver and antenna gear drive unit which transforms a complicated timeconsuming installation process into one that can be handled by those inexperienced in the art, such as first time purchasers of TVRO systems. The antenna drive unit includes a first motor and an associated gear train for driving the dish in an azimuth direction, and a second motor with an associated gear train for driving the dish in an elevational direction. With a two-motor drive system, the antenna can be moved and oriented in a much wider range of positions than with the single azimuth drive achieved by the linear actuator of the prior art. Additionally, as the gear units are self-contained and are comprised of substantially circular or spur gears, there is a linear relationship between the movement of the dish and the movement of the motor shafts or any of the associated gears such that the position of the dish can be accurately determined both initially, and as the dish continues to operate over time. It is significant that there are no worm gears in the drive unit. Generally worm gears are used to minimize backlash and slippage in the gears which leads to mispointing of the antenna and a deterioration of the signal and picture displayed. However, worm gears require expensive materials and construction whereas the ring and spur gears of the present design may be made of injection molded plastic. Backlash and gear slippage is minimized through the enormous reduction ratios present in the gearing.
Still another feature of the present invention is the microprocessor based receiver which has means to store the necessary data to correctly calculate and automatically position the antenna at each of the available satellites merely upon an operator's entry of the antenna site location in latitude and longitude. Additionally, automatic peaking routines are available under operator command through the remote control to peak each antenna position for maximum signal strength. This is typically done upon initial installation, and at periodic intervals or when the operator might suspect a shifting has occurred such that there is a deterioration in picture or sound quality. Once these "peaked" positions are obtained automatically, they are stored by the operator and provide the position data to repoint the antenna at each of the satellites during normal day-to-day operation.
Still another feature of the present invention is a peaking program under operator control which eliminates skew by rotating the probe to a signal null and then repositioning the probe 90.degree. away from the null to maximize signal strength. As nulls are much more sharply defined than the peak signal point in the spectrum, physically locating the null point and then rotating 90.degree. from that null point results in a more accurate alignment of the probe to eliminate skew. As is known in the art, skew results from misalignment of the probe with respect to the incoming horizontally or vertically polarized signal. Skew is present at each of the various positions of the antenna as the satellites lie on an arc while the antenna is physically located on a surface well above the focal point of that arc. Therefore movement of the dish from satellite-to-satellite results in a misalignment of the probe with respect to the satellite, thereby requiring skew adjustment.
While the various features of this invention may be separately utilized in connection with other compatible pieces of equipment manufactured by others, the gear drive unit of the present invention permits the receiver to utilize its entire capability by accurately positioning the satellite in the azimuth and elevation direction, as well as to adjust the skew of the probe to absolutely maximize the quality of the picture and sound received from the satellite. This can be important because of the great variation in signal strength from satellite-to-satellite as one moves from point-to-point throughout North America. All satellites have a "footprint" which defines the area of acceptable power within which they can be received. Therefore, to maximize the available programming for any particular geographic location, the additional features and benefits of the present invention maximize the opportunity to receive as much programming as possible.
While the foregoing has been a brief description and summary of some of the principal advantages and features of the present invention, a more complete understanding and appreciation for the invention may be obtained by referring to the drawings and description of the preferred embodiment which follows.